US Patent Publication No. 2009/0151738, incorporated herein by reference, discloses a degradable cigarette filter where the degradation is obtained by materials that catalyze the hydrolysis of the cellulose acetate filament. Cellulose acetate used in the filaments of cigarette filters typically has a Degree of Substitution (D.S.) in the range of 2.0-2.6. Cellulose acetate with a D.S. in the range of 2.0-2.6 is not readily attacked by naturally occurring enzymes and bacteria; however, cellulose acetate with a D.S. of ≦1.0 is vunerable to attack by naturally occurring enzymes and bacteria. To reduce the D.S. of the cellulose acetate, the cellulose acetate must be hydrolyzed (i.e., replacement of the acetate moieties with hydroxyl moieties).
In US Patent Publication No. 2009/0151738, one method for carrying out the invention was the use of a pill (or pills) dispersed into the tow. These pills comprised the hydrolysis catalyst being coated with the water soluble material. These pills worked as expected and the cellulose acetate tow was hydrolyzed and then degraded. However, this simple construction was defficient in two ways; first, the catalyst was too quickly released, and second, the pill was a foreign object that could negatively impact the taste of the smoke. The release of catalyst too quickly can lead to the complete loss of catalyst before hydrolysis (or sufficient hydroysis) can occur, whereby the purpose of the invention is defeated.
Accordingly, there is a need for a new pill construction that provides for the controlled and sustained release of the hydrolysis catalysis and that will not negatively impact the taste of the cigarette smoke.